The present disclosure relates generally to compositions and methods for therapeutic delivery. More particularly, the present disclosure relates to nanoparticle compositions that sequester a target molecule, methods for targeted delivery of a target molecule, methods for thrombus (blood clot) dissolution and methods for inducing blood clotting.
During injury of a blood vessel, aggregated platelets and cross-linked fibrin form a blood clot (thrombus) to prevent blood loss. The coagulation process is useful in closing up and maintaining the platelet plug on larger wounds. Though blood clotting is necessary for wound healing, it has the ability to cause severe health problems if the thrombus becomes detached and travels through the circulatory system. Particularly, acute vascular thrombosis, including coronary, cerebrovascular, and pulmonary thrombosis, causes more deaths than any other disease process in Western society. Thrombosis is the formation of a blood clot inside a blood vessel, which obstructs blood flow through the circulatory system. An embolus can also become lodged within a blood vessel and obstruct blood flow. Death of tissue can result when blood flow is cut-off in a blood vessel that supplies the tissue. If the thrombus reaches the heart, brain or lungs, it could lead to heart attack, stroke, or pulmonary embolism.
Treatment and prevention of blood clots involve the inhibition of clot formation and growth. Heparin, for example, binds to and activates antithrombin to inhibit the formation and growth of clots. Warfarin, for example, inhibits vitamin K epoxide reductase, which is needed for the synthesis of clotting factors such as prothrombin and factor VII. Other treatments involve dissolving blood clots (thrombolysis). For example, streptokinase and urokinase are administered intravenously and can be used to dissolve blood clots. Tissue plasminogen activator converts plasminogen into plasmin. Activated plasmin, in turn, cleaves cross-linked γ-chains in the D-domain of fibrin (Aα 148-460) to effectively digest the thrombus. Plasminogen is a 91 kDa zymogen containing 791 amino acids, produced in-vivo by the liver, and is heavily glycosylated (2% carbohydrate) in its circulating form (FIG. 1). When cleaved at Arg561-Val562, plasminogen produces plasmin, a serine protease with a trypsin-like active site. Plasmin binds to thrombi via electrostatic attraction between its five kringle (K) domains to the exposed lysine residues on fibrin with a Kd=0.5 μM for lys-plasmin and Kd=5 μM for glu-plasmin. In order, K4 has the least, K1-K3 have moderate, and K5 has the highest affinity fibrin binding. Plasmin's activity is rapidly neutralized in plasma by the circulating proteins α2-antiplasmin. Cl-inhibitor, and macroglobulin. The serpin α2-antiplasmin provides the most rapid and avid inhibition, whereby an Arg-Met residue binds directly to the serine residue in plasmin's active site with a rate constant of 4×107 M−1 Sec−1.
Lack of target specificity poses the largest threat to the clinical therapeutic index of the plasminogen activators. Even when rt-PA is infused directly via a catheter buried within the thrombus, some degree of systemic plasminogen activation occurs, resulting in fibrinogenolysis and increased bleeding risk.
Alternatively, the inability of blood to clot can lead to excessive bleeding. Bleeding disorders, such as hemophilia and Von Willebrand disease, are characterized by longer bleeding episodes. Longer bleeding episodes can result in longer wound healing time, deep internal bleeding, joint damage, intracranial haemorrhage and shorter life expectancy. Additionally, bleeding injuries can sometimes require administration of a hemostatic agent to induce blood clot formation to stop blood loss. Antihemorrhagic agents work by inhibiting fibrinolysis or promoting coagulation. Examples of antihemorrhagic agents include antifibrinolytics, blood coagulation factors, fibrinogen, collagen, vitamin K and chitosan. Topical hemostatic agents are also available for use in inducing blood clot formation.
While the compositions and methods described above are suitable for preventing and treating blood clots, prevention of clotting can lead to excessive bleeding and some drags can be non-specific to fibrin and digest other proteins. Accordingly, there exists a need to develop compositions and methods for treating blood clots in instances where severe health problems arising from the blood clot can develop. While hemostatic agents and topical applications are available for promoting blood clot formation, they are systemically administered, and thus, ma suffer from degradation prior to reaching the injury site or require direct access to the injury. Accordingly, there also exits a need for alternative compositions and methods to induce blood clot formation to avoid excessive bleeding in individuals with bleeding disorders or bleeding injuries.